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Oldest known fossil animal that is generally accepted as a bird (classified as genus Archaeopteryx). It flourished during the Late Jurassic period (159–144 million years ago). Fossil specimens indicate that archaeopteryx ranged in size from as small as a blue jay to as large as a chicken. Archaeopteryx shared anatomical characteristics with both birds (well-developed wings and birdlike skull) and theropod dinosaurs (well-developed teeth and a long tail).
This entry comes from Encyclopædia Britannica Concise. For the full entry on archaeopteryx, visit Britannica.com.